1. Field of Invention
This invention relates to typewriters, particularly to a typewriter having tabulation (tab) controls. More particularly it relates to such typewriter wherein reverse as well as forward tab capabilities are provided.
2. Description of Prior Art
Heretofore most typewriters contained tab controls for rapidly and automatically adjusting the relative positions of the printing mechanism (type bars or print head) and the platen. In typewriters with fixed print heads or typebars, the platen was moved with respect to printing mechanism, and in typewriters with fixed platens, the printing head (a ball or a spoked and rimless "daisy" wheel) was moved with respect to the platen. For purposes of facilitating discussion, the operation will be detailed with reference to the latter type of machine (the print head moves and the platen is fixed), but the former type of machine (print mechanism is fixed and platen moves) should also be considered as an included method of tab operation.
The tab feature is useful for enabling a typist to effect rapid and repetitive movements of the printing mechanism to a plurality of different horizontal positions along a line on the paper or other recording web. In mechanical typewriters, the tab stop positions were usually stored by positioning mechanical pawls to stop movement of the platen at spaced horizontal locations, where desired. In electronic typewriters, the output of the keyboard consists of electronic signals which are processed in an electronic data processing system within the typewriter to generate suitable control signals for driving solenoids and step- or servo-motors to cause the typing mechanism to print selected characters and effect other operations; here the tab stop positions usually were stored in an electronic memory and the carrier was moved to the tab stop positions by means of a servomechanism under control of the electronic data processing system.
In most typewriters, the tab system was of the forward type only, i.e., the tab mechanism was able to move the printing mechanism only to the right with respect to the platen. This is disadvantageous in situations where a typist must type, for example, a single column of characters. After typing a line of the column, to type the next line the typist must return the print head to the first character of the column. To do this, the typist must choose one of two awkward alternatives. The first alternative is to reset the left margin control to the first character of the column of characters before typing the column. However this is an awkward operation and the original margin must be located and restored when typing of the column is completed. Alternatively, the typist can effect a carrier return, causing the carrier to move all the way to the left, and thereafter repeat tab until the carrier advances to the desired position; this is also awkward and inefficient.
To avoid these drawbacks, typewriters recently have appeared with a reverse-tab capability. In these typewriters, when a reverse-tab key was pressed, or when the regular tab was actuated in a certain manner, different from the regular forward-tab method of actuation, the carrier would move to the left with respect to the platen, i.e., to the next tab stop at the left of its current position. The reverse-tab feature greatly facilitated typing of columnar material by eliminating the above drawbacks.
As an added feature, some typewriters have also provided an automatic line indexing or platen rotation feature upon operation of the reverse tab key. In this feature, when the reverse tab key was operated and the carrier moved to the left with respect to the platen, the platen would also index, i.e., rotate by an angle equivalent to one line space so as to cause the next line position on the paper to appear at the current typing position. This made it even easier to type columnar material since it eliminated the need for the typist to manually advance to the next line space after a reverse-tab operation.
However the above combination of indexing or line spacing with reverse tab was disadvantageous when several columns of material were being typed since this requires that the carrier be moved to a second or even further-left column from a current typing position after each line is typed. The typist was not able to do this easily by repetitively reverse tabbing because every reverse-tab also caused an index; thus the correct position for typing the next line would be lost upon the second reverse-tab actuation. Thus in order to effect a reverse-tab movement to a second or subsequent column, the typist had to repetitively reverse tab to the desired column and thereafter adjust the platen so that the correct line on the paper was at the printing position. Alternatively, the typist could still effect a carrier return to the left margin and then forward tab to the desired column. However this did not take advantage of the machine's reverse-tab capability and was also difficult and time consuming.
Accordingly, one object of the present invention is to provide a typewriter with a reverse-tab feature whereby reverse-tab operation to the second or further columns of typing material to the left of the current position can be effected without adjusting the platen. Another object is to provide such a typewriter with a more efficient reverse-tab operating sequence. A further object is to provide an electronic typewriter with a novel reverse-tab operating feature. Still further objects and advantages will become apparent from a consideration of the ensuing description and the accompanying drawing.